Timeline for Using Doppler velocimetry with digital signals such as Bluetooth
Current License: CC BY-SA 3.0
11 events
| when toggle format | what | by | license | comment | |
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| Nov 6, 2013 at 20:43 | comment | added | nispio | That's right, there will be no hopping while the device is in "pairing mode." However, if the device you want to "listen to" is already paired with another device, then it will already be hopping frequencies and you might not be able to "get a lock" on it. (Sorry for the vagueries and non-technical terms. One of the frustrating things about working with BT is that the Bluetooth Standard uses completely different language than the common BT terms we are used to.) | |
| Nov 6, 2013 at 20:34 | comment | added | ian | For anybody following this post in the future I have just discovered that frequency hopping only occurs after a connection has been established. There is no frequency hopping while a peripheral is advertising. | |
| Oct 30, 2013 at 20:37 | comment | added | nispio | Much more difficult if you are not paired. In isolation, you could just watch the spectrum and see where the activity occurs. However, in the presence of other wireless devices operating in this band, it might be hopeless. If you happened to be "listening" at the time the pairing occured, you might be better off, but my understanding of the BT spec is too limited to say exactly what you could and could not achieve. | |
| Oct 30, 2013 at 20:32 | comment | added | ian | Oh i see. It is predetermined. What if they are not connected meaning that the peripheral device is just advertising the information and the central device is picking it up. Would the central device be able to determine the expected frequency hop and from there break it down into pulses and find a solution for the doppler shift? | |
| Oct 30, 2013 at 20:18 | comment | added | nispio | The bluetooth spec defines how the frequency hopping occurs, and it is not trivial. However, the receiving bluetooth device is synchronized with the transmitting bluetooth device at pairing time in such a way that it always knows what frequency the transmitter will hop to next. Otherwise, how would it know where to listen for the next packet? | |
| Oct 30, 2013 at 20:05 | comment | added | ian | This may sound dumb, but how could I know how the transmitted signal should have looked like? Is the transmitted signal's "expected" frequency hopping sequence contained in one of the transmitted packets? | |
| Oct 30, 2013 at 19:53 | comment | added | nispio | In fact, with regards to the frequency hopping, it probably has some analogies to pulse-doppler radar. Once you have the decoded, demodulated data, you know exactly what the transmitted signal should have looked like. If you view each frequency hop as a separate pulse, you can coherently combine the information from each of the short pulses to converge on a solution. | |
| Oct 30, 2013 at 19:47 | vote | accept | ian | ||
| Oct 30, 2013 at 19:45 | comment | added | nispio | All of that is true, but that is not why you can't do it on an iPhone. Since the frequency hopping is deterministic, you could still get the information you need out of the raw data, if the raw data was available to you. | |
| Oct 30, 2013 at 19:41 | comment | added | ian | I was told that I could not use doppler velocimetry with Bluetooth because according to bluetooth.com: Bluetooth technology operates in the unlicensed industrial, scientific and medical (ISM) band at 2.4 to 2.485 GHz, using a spread spectrum, frequency hopping, full-duplex signal at a nominal rate of 1600 hops/sec. … adaptive hopping among 79 frequencies at 1 MHz intervals gives a high degree of interference immunity and also allows for more efficient transmission within the spectrum. Aside from not be able to use the iphone to do it. is this true? | |
| Oct 30, 2013 at 18:54 | history | answered | nispio | CC BY-SA 3.0 |